Crown and bridge prosthodontics is the science and art of the complete restoration of one or more teeth and the replacement of one or more natural teeth with an artificial device. A bridge is used to replace at least one missing tooth and is supported by natural teeth. The bridge includes a pontic which fills the edentulous space between abutment teeth and a connector which joins the pontic to a bridge retaining member such as a crown formed on each abutment tooth adjacent the pontic.
The primary purpose of the dental bridge is to receive the forces of occlusion and to transmit them through the abutments so that occlusion is restored to the patient, thereby contributing to mastication. The bridge should also augment the ability of the patient to enunciate and maintain the position of the teeth relative to opposing teeth. The present day construction of a dental bridge is a time consuming, involved and complex process which requires the application of many independent procedures including the following: waxing, spruing;, investing, casting, cleaning, trimming, cutting and stoning. The process, as conventionally practiced, is referred to colloquially as the "lost wax casting method" and is currently the universally accepted procedure for making a bridge. The bridge retaining member(s) and pontic may be cast as one piece or each may individually be cast and joined by soldering. The preparation for casting and the casting process must be meticulously followed with the technician paying strict attention to detail, particularly during the wax-up, investment, spruing and casting operations to assure accuracy of the cast product and proper fit. If the fit is not accurate, it will, in most cases, be necessary to recast the bridge which substantially increases the time spent both by the dentist and dental technician in completing the restoration.
In the construction of a fixed bridge, it is customary to cast the bridge retaining member(s) and the pontic separately and then to unite the pontic to the retaining member(s) by a solder connection on an investment model. The strength of a dental bridge formed by soldering the bridge elements together is dependent upon the strength of the solder joint and the bond formed between the solder joint and bridge retainer. A bridge with a weak solder connection is susceptible to early failure.
It has been discovered in accordance with the present inventon that a pontic can be joined to a bridge retaining member using a combination of welding and soldering to provide a connection between the pontic and bridge retaining member which is substantially stronger than a soldered connection and which does not require casting in constructing the bridge or, in fact, any individual member of the bridge. Moreover, the method of the present invention makes it much easier to form an acceptable solder connection and with less skill. Welding is not currently practiced in the construction of a crown and bridge since welding causes the base metal to melt whereas in soldering only the solder material is melted.
The method of the present invention is particularly suited to the construction of a dental bridge in which the pontic is united to a prefabricated bridge retainer constructed from relatively thin metal foil without casting. In fact, in accordance with the present invention, neither the bridge retainer(s) nor the pontic need be cast and each may be of a prefabricated construction with relatively little constraint in the amount of metal used or its thickness. The method of the present invention in conjunction with the use of non cast metal bridge retainer(s) eliminates casting from dental bridge construction in its entirety.
A dental prosthesis assembly has also been developed to facilitate the construction of a dental bridge, without casting, from prefabricated metal retainer(s) and a prefabricated pontic. The dental prosthesis assembly of the present invention comprises a metal pontic constructed with an arm rest extending from opposite ends thereof for suspending the pontic between bridge retainers mounted on adjacent abutment teeth to form a bridge therebetween and a metal spacer for joining each arm rest to each corresponding bridge retainer through a welding operation. Each metal spacer is preferably composed of at least several layers having at least one layer of high fusing temperature metal. The metal spacers are adapted to be interposed between each arm rest and each bridge retainer to permit the arm rest to be spot welded to the retainer. The dental prosthesis assembly is modified in accordance with the present invention to form a splint for bracing two or more teeth without casting. In such instance, a pontic is not required and the splint is formed using opposing arm rests extending from a common joint. The arm rests are spot welded to the bridge retainers through the metal spacers.